ES6里变量规范

• 默认const
• 需要重新赋值时用let
• 尽量避免var

let

• 局部变量
• 可重新赋值

var name='let' //window.name的值会改变
//---------------------------
let name='let' //window.name不受影响

{
    let a=1
    console.log(a)
}
console.log(a);//Uncaught ReferenceError: a is not defined

const

const  b=1
b=2;// Uncaught TypeError: Assignment to constant variable


const obj={a:1,b:2};
//obj={a:3,b:4}  //Assignment to constant variable
//可修改属性
obj.a=111
obj.c=3;

//freeze后下面的修改不起作用
Object.freeze(obj)
obj.a=123
obj.d=444